JAVA NOTES

CONTENTS

• General Notes
• Specifics
• Learning Curriculum
• Mockito

RELATED LINKS

• springboot_logapp

General Notes

• TO RUN the code, you need to first
  • javac myProg.java then
  • java nameOfMyEntryClassWithMainInIt and ignore the .java
• Two classes in same file means only one can have public
• If you have multiple files imported, you need to compile them all at the same time javac BankAccount.java SavingsAccount.java CheckingAccount.java
• If you have all java files at same level you don't need import statements

Specifics

Optional

When you return an Optional object, you are returning an instance of the Optional class that wraps the actual value (which can be an object or a null). The Optional class is used to better handle cases where a value might not be present, which helps prevent NullPointerExceptions.

set it like this

 Optional<String> result1 = getString(true);

// .....

// returning 

     public static Optional<String> getString(boolean hasValue) {
        if (hasValue) {
            return Optional.of("Hello, world!");
        } else {
            return Optional.empty();
        }
    }

Return looks like

Result 1: Hello, world!
Result 2 is empty

Constructor

Must have the same name as the class Don't give it a type, its just

public Car(String make, String model, int year){

	}

Methods

Define the return type

// Methods
public double getArea() {
    return Math.PI * radius * radius;
}

Set methods that don't return anything must have void as the type

    public void setRadius(double radius) {
        this.radius = radius;
    }

Super

• If extending you need to construct parent variables even if you don't use them

package com.example.bank;

public class CheckingAccount extends BankAccount{
    public double overdraftLimit;

    // you HAVE TO construct all parent variables even if you don't use them 
    public CheckingAccount(double balance, String accountNumber, double overdraftLimit){
        super(balance, accountNumber);
        this.overdraftLimit = overdraftLimit;
    }

    @Override
    public void withdraw(double amount){
        double balance = getBalance();
        if(balance-amount >= overdraftLimit){
            super.withdraw(amount);
        } else{
            System.out.println("withdrawal Denied: Exceeds overdraftLimit.");
        }
    }
}

Learning Curriculum

Each part can be found within the folder at the base of this project with the similar name. For example the classes have a list of projects, cylinder, square, circle etc all have examples of this.

Classes, Constructors, methods and objects

Learn how to create classes, with variables, construct self variables, create methods and instantiate them inside a main class then log the output.

Inheritance and Polymorphism

Learn how to create and use subclasses and understand the concepts of inheritance, overriding, and polymorphism. This will help you design more efficient and reusable code.

Interfaces and Abstract Classes

Understand the purpose of interfaces and abstract classes, and learn how to create and use them in your code. This will allow you to design more flexible and modular programs.

Collections Framework

Explore the Java Collections Framework, which provides a variety of data structures like ArrayList, LinkedList, HashSet, HashMap, etc. This will help you to choose the right data structure for a specific task and improve the efficiency of your programs.

Exception Handling

Learn how to handle exceptions in Java using try-catch-finally blocks and how to create custom exceptions. Proper exception handling can make your programs more robust and fault-tolerant.

Java I/O

Learn about Java I/O classes and methods for reading and writing data from/to various sources like files, network sockets, etc.

Concurrency

Understand Java threads and concurrency concepts, including synchronization and thread communication. This will help you create more efficient and responsive applications, especially when dealing with multi-threading.

Java Networking

Learn about Java networking concepts and how to create client-server applications using Java sockets.

Java GUI Programming

Explore Java GUI programming using JavaFX or Swing libraries. This will allow you to create user-friendly graphical interfaces for your applications.

Java Database Connectivity (JDBC)

Learn how to interact with databases using Java JDBC. This will enable you to create data-driven applications.